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Emergency managers fine-tune hurricane evacuations

Traffic backed up when residents evacuated Houston as Hurricane Rita approached. Emergency managers are testing new tools to help decide when to order residents out of harm's way.

AP ARCHIVE / 2005

KATE SPINNER

Published: Monday, March 26, 2012 at 11:51 p.m.

Last Modified: Monday, March 26, 2012 at 11:51 p.m.

ORLANDO - Emergency managers are testing new tools to help them decide when to order evacuations ahead of potential flooding from hurricanes.

Experts say the old method — based only on a storm's predicted speed at landfall — is too simplistic when it comes to deciding which areas should be evacuated and when. As a result, evacuations are often ordered unnecessarily.

But Lee County is working with other local governments to develop a chart designed to match a hurricane's projected flood threat with the vulnerability of various areas.

The chart is based on odds that shift as a hurricane approaches land. As the odds of flooding increase for different areas, emergency managers will know when they should order an evacuation.

Emergency officials discussed the chart at the National Hurricane Conference here on Monday.

Lee County Public Safety Director John Wilson said officials need to consider assessing the risk of flooding and the danger posed by wind separately in making evacuation decisions.

Low-lying areas may be safe from catastrophic wind damage, but still vulnerable to flooding from storm surge, for example.

In Southwest Florida, the biggest threat from hurricanes is usually storm surge, caused when the force of a hurricane's wind pushes the sea over land. The amount of flooding from surge depends on a property's location near the coast, the land elevation and the storm's size, strength, speed and angle of approach.

Under the worst case scenarios, hurricanes can push the sea more than 24 feet higher than normal — or more — in most Southwest Florida counties. If such a storm threatens part of Lee County, everyone in pre-determined evacuation zones there would need to leave, even if the chances of that catastrophic surge were only 1 in 5, or 20 percent. That risk is too high, according to Lee County's chart.

The chart lists the possible amount of flooding from a storm in the top row and the chances that the storm will cause that amount of flooding in a column. The evacuation zones — listed A through E — fall into place within the chart, with the A zones evacuating from the least-severe flood and the E zones evacuating from the worst-case scenarios.

For instance, anyone in an A zone — on the waterfront or barrier islands — would need to evacuate if a storm had a 10 percent chance of pushing the tide six feet higher than normal. On the other end of the spectrum, the A zone would also need to evacuate from a less-severe, three-foot surge if chances of that flood were 90 percent.

The Lee County evacuation chart has yet to be tested in a hurricane, but it has the interest of the National Hurricane Center and other counties in the region, Wilson said. He said Pinellas County and Sarasota County are looking at creating similar charts based on their own risks.

<p><em>ORLANDO</em> - Emergency managers are testing new tools to help them decide when to order evacuations ahead of potential flooding from hurricanes.</p><p>Experts say the old method — based only on a storm's predicted speed at landfall — is too simplistic when it comes to deciding which areas should be evacuated and when. As a result, evacuations are often ordered unnecessarily.</p><p>But Lee County is working with other local governments to develop a chart designed to match a hurricane's projected flood threat with the vulnerability of various areas.</p><p>The chart is based on odds that shift as a hurricane approaches land. As the odds of flooding increase for different areas, emergency managers will know when they should order an evacuation.</p><p>Emergency officials discussed the chart at the National Hurricane Conference here on Monday.</p><p>Lee County Public Safety Director John Wilson said officials need to consider assessing the risk of flooding and the danger posed by wind separately in making evacuation decisions.</p><p>Low-lying areas may be safe from catastrophic wind damage, but still vulnerable to flooding from storm surge, for example.</p><p>In Southwest Florida, the biggest threat from hurricanes is usually storm surge, caused when the force of a hurricane's wind pushes the sea over land. The amount of flooding from surge depends on a property's location near the coast, the land elevation and the storm's size, strength, speed and angle of approach.</p><p>Wilson's evacuation grid guides evacuation decisions based on those storm surge threats.</p><p>Under the worst case scenarios, hurricanes can push the sea more than 24 feet higher than normal — or more — in most Southwest Florida counties. If such a storm threatens part of Lee County, everyone in pre-determined evacuation zones there would need to leave, even if the chances of that catastrophic surge were only 1 in 5, or 20 percent. That risk is too high, according to Lee County's chart.</p><p>The chart lists the possible amount of flooding from a storm in the top row and the chances that the storm will cause that amount of flooding in a column. The evacuation zones — listed A through E — fall into place within the chart, with the A zones evacuating from the least-severe flood and the E zones evacuating from the worst-case scenarios.</p><p>For instance, anyone in an A zone — on the waterfront or barrier islands — would need to evacuate if a storm had a 10 percent chance of pushing the tide six feet higher than normal. On the other end of the spectrum, the A zone would also need to evacuate from a less-severe, three-foot surge if chances of that flood were 90 percent.</p><p>The Lee County evacuation chart has yet to be tested in a hurricane, but it has the interest of the National Hurricane Center and other counties in the region, Wilson said. He said Pinellas County and Sarasota County are looking at creating similar charts based on their own risks.</p>